This invention relates in general to the aeration of waste water and more particularly to a plastic diffuser which discharges air into waste water in the form of relatively large bubbles.
The treatment of waste water involves, among other things, aerating the waste water in order to transfer oxygen to it. In the past, the aeration function has been performed by a variety of different types of diffusers, including fine bubble diffusers, flexible membrane diffusers, porous tube diffusers, dome diffusers, and coarse bubble diffusers. Although coarse bubble diffusers are not particularly efficient in transferring oxygen to the water because of the relatively large size of the bubbles, they are advantageous in other respects, most notably in that they have low maintenance requirements. Thus, coarse bubble diffusers are used primarily in systems where low maintenance is especially important.
As disclosed in U.S. Pat. No. 3,953,553, it is beneficial to employ what may be referred to as a wide band diffuser geometry in which diffusers are installed perpendicular to the lateral pipe. Maximum diffuser floor coverage and maximum wide band diffuser activity are provided. In this type of arrangement, long diffusers with maximum bubble release area are desirable. Coarse bubble diffusers that mount on top of the pipe are possible but are less economical and less efficient than the wide band approach.
The connection of coarse bubble diffusers to the air lateral piping has presented significant problems. Threaded connections suffer from structural weakness that can cause premature failure, especially when relatively long diffusers are used and the diffuser length increases the loading on the connection due to the increased leverage effect that results from increased diffuser length. In addition, the rotative position of the diffuser can vary when a threaded connection is used, and the diffuser can thus be oriented improperly and have no adjustment. Moreover, threaded connections involve abrupt changes in diameter from the fitting diameter to the diffuser diameter, causing a stress concentration that has required castings rather than weldments to be used.
Stainless steel is typically employed as the material of which generally tubular wide band coarse bubble diffusers are constructed. Stainless steel diffusers require metal fittings which are typically stainless steel for corrosion resistance. There is no ability to add or subtract diffusers in the field, there is a need for factory fabrication of the pipe and shipment specifically to the job site, and salts and chemicals in the waste water can degrade the metal.
The present invention is directed to a plastic coarse bubble diffuser that is improved in a number of respects in comparison to the tubular wide band coarse bubble diffusers that have been used in the past. It is a particular object of the invention to provide a coarse bubble diffuser that is constructed to be mounted to the aeration system piping in a secure manner without special pipe fabrication techniques or fittings. In this regard, a mounting arrangement of the type disclosed in pending application Ser. No. 340,265, filed Apr. 19, 1989 may be used, and the diffuser may be glued to the mounting tee to provide a full 3" diameter connection that is strong enough to withstand the considerable forces that are applied to the diffuser in service. Additionally, the diffuser is secured in the proper position, is adjustable and cannot inadvertently rotate or otherwise become improperly oriented. The diffuser and mounting bracket can be installed on any type of pipe having iron pipe diameter, including polyvinyl chloride, stainless steel, steel, ABS and the like. Attachment does not require special outlets or fittings but instead requires only that a hole be drilled to accept the mounting saddle. These features are achieved by providing a cylindrical inlet end on the diffuser body for connection with the tee outlet of the mounting arrangement, or with another fitting having a circular outlet to which the diffuser inlet can be solvent welded. The construction of the diffuser from polyvinyl chloride or a similar plastic material permits solvent welding of the connection permanently in the proper orientation, as compared with prior screw in diffusers that are often installed too tightly or too loosely to create operational problems.
Another object of the invention is to provide a coarse bubble diffuser in which maximum liquid velocity across the outlet openings is achieved. This feature is accomplished by providing the diffuser body with flat side walls. The air which exits from the outlet openings in the side walls is subjected to maximum shear because of the high liquid velocity that results from the flat shape of the side walls. Consequently, the air bubbles are maintained as small as possible for the size of the outlet openings, and the oxygen transfer efficiency is enhanced accordingly.
A further object of the invention is to provide a coarse bubble diffuser of the character described in which the air dispersion along the length of the diffuser is uniform.
Still another object of the invention is to provide a coarse bubble diffuser of the character described in which the diffuser body has an end ca that can be conveniently removed to allow inspection and/or cleaning of the diffuser interior. The downstream end of the diffuser body has a cylindrical shape so that the end cap can simply be threaded into and out of the diffuser or another type of removable end plug can be conveniently employed.
An additional object of the invention is to provide a coarse bubble diffuser of the character described having a diffuser body that is strong enough to withstand the forces to which it is subjected while in service. Despite the two transitions that are required between the flat wall center section of the diffuser body and the cylindrical opposite ends, the construction and configuration of the diffuser provides transition areas that avoid abrupt changes in the wall thickness diameter of connections or the creation of any weak points near the inlet end where stresses are concentrated. A full three inch connection is used rather than 3/4 nipples or other weak connections.
Yet another object of the invention is to provide a coarse bubble diffuser of the character described which is suitable for use as an open bottom unit or a unit which is equipped with a deflector at the bottom to deflect large solids such as rags and the like.
Still another object of the invention is to provide a coarse bubble diffuser of the character described which is simple and economical to construct, which can be easily installed in the field without the need for special tools, and which has low maintenance requirements.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.